Don't go to Merrifield. We had them plants tens of thousands of dollars worth of their trees, one was dying, and they claimed it had something to do with something not connected to them. Which is odd, since they sold us the trees and they planted the trees themselves.
They could have comped one tree out of so many, but they chose not to, so we tell our friends not to go there, especially for the money.
There are tons of smaller nurseries (less overhead!) on route 50/29, toward Fairfax, I would try them.